Catalytic in situ combustion



United States atent Fatented Aug. 7, 12

3,048,225 CATALYTIC IN SllTU COMEUSTION Alfred D. Reichle, Baton Rouge, La, assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Aug. 23, 1959, Ser. No. 836,596 7 Claims. (Cl. led-11) This invention relates to a precess for the catalytic in situ combustion of hydrocarbon-containing strata. A specific aspect of the invention pertains to a process for depositing iron-containing catalyst in the combustion area of such strata.

In situ combustion in the recovery of hydrocarbons from underground strate containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein followed by injection of air thru the ignition borehole and recovery of product hydrocarbons and combustion gas thru another borehole in the stratum is a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum frequently plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the cool stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difiiculty and to permit the continued progress of the combustion zone thru the stratum, inverse. air injection has been resorted'to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes, causing the combustion zone to move toward the injection boreholes. Production is recovered thru the ignition borehole.

In situ combustion techniques are being applied to tar sands, shale, Athabasca sand and other strata in virgin state, to coal veins by fracturing, and to strata partially depleted by primary and even secondary and tertiary recovery methods.

Recovery of hydrocarbons from carbonaceous strata, such as various types of oil and tarsands, porous and fractured coal veins, and other permeable carbonaceous deposits is a rather slow process and consumes an appre ciable proportion of the carbonaceous material as fuel during the process. It has been found that the in situ combustion process can be speeded up and the combustion temperature can be decreased so that a smaller proportion of the carbonaceous deposit is consumed in the process, thereby producing a greater amount of hydrocarbons and fuel gas from the deposit in a shorter period of time. Catalysts, particularly, iron-containing catalysts, have been utilized to achieve these improvements. The deposition of the catalyst in the stratum is one of the problems arising in this technique. One method of depositing ironcontaining catalysts in a stratum requires the injection of an aqueous solution of an iron salt into the stratum so as to deposit the iron compound in the stratum prior to the initiation of combustion therein. This process is time consuming and expensive, even though it is economically feasible in most applications.

This invention is concerned with an improved method of utilizing an iron-containing catalyst in an in situ combustion process.

Accordingly, it is an object of the invention to provide an improved process for producing hydrocarbons from a carbonaceous stratum by in situ combustion. Another object is to provide an improved method of utilizing an ironcontaining catalyst in an in situ combustion process in the production of hydrocarbons from a permeable carbonaceous stratum. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises injecting combustion-supporting gas containing iron carbonyl in gas or vapor form into the combustion zone in a carbonaceous stratum in the area just in advance of the combustion front so as to decompose the iron carbonyl into Fe and CO, whereby the iron is deposited in or adjacent the leading edge of the combustion front where it catalyzes the combustion reaction. In order to deposit the iron in the stratum where it will catalyze the combustion process, it is essential to move the combustion front thru the stratum by inverse injection of combustion-supporting gas. The usual method involves igniting a carbonaceous stratum around an ignition well therein and injecting air (or other combustion supporting gas, such as oxygen, oxygen-enriched air, etc.) thru one or more offset wells so that the air moves into the combustion zone countercurrently to the movement thereof.

There are three forms of iron carbonyl, viz., the pentacarbonyl, Fe(CO) the tetracarbonyl, Fe(CO) and the nonacarbonyl, Fe (CO) All of the iron carbonyls are volatile and decompose at temperatures between atmospheric and the combustion temperature of hydrocarbons so that when injected with the inverse air, they are decomposed into Fe and CO in the warm stratum adjacent the leading edge of the combustion zone. To illustrate, iron pentacarbonyl has a vapor pressure of 40 mm. Hg at 30? C., is stable in air in the dark at ordinary temperatures, and begins to decompose to Fe and CO at about 60 C., being completely disassociated at 200 C. Iron pentacarbonyl can be readily incorporated in the injection air by passing the air over liquid pentacarbonyl at atmospheric temperature or at slightly higher temperatures, preferably, below about 40 C. A concentration of the iron carbonyl in the injection air in the range of about .05 to 1.5 volume percent is effective in increasing the propagationrate of the combustion front and lowering the temperature of the combustion, although greater amounts may be utilized with good results. However, the cost of the carbonyl is an economic factor to be reckoned with and the process and concentrations in the lower part of the range are satisfactory and more economical.

In practicing the invention it is desirable to dry out the stratum within the well pattern to be produced before igniting the stratum. In the event a ring pattern is used, air or other drying gas may be injected thru the central well to produce water thru the ring of offset Wells, or the air may be injected thru the wells in the ring to produce water thru the central well. After the formation is dried out, ignition is initiated around the central well by any suitable means, such as by burning a fuel pack (charcoal) in the ignition well adjacent the stratum and driving a combustion zone thru the stratum by injecting air or other combustion-supporting gas thru the wells in the ring with production being recovered thru the central ignition well. Of course, iron carbonyl in suitable concentration is injected with, or otherwise incorporated in, the air being injected so that the deposition of iron in the stratum in advance of the combustion zone or in the leading edge thereof is efiected.

It is not known whether the iron is converted to iron oxide but this is believed to be the case. However, the invention is not predicated upon any theory or assumption with respect to the exact form of the iron when it exerts its catalytic effect.

It has been found that the temperature in the combustion zone is reduced as much as about 70 to 100 F. by the use of iron-containing catalyst and the rate of movement of the combustion front thru a tar sand, for instance, is increased by about 15 percent.

In accordance with another method of operation, combustion of the stratum is initiated around each well in a line of ignition wells as by igniting the stratum around alternate wells in the line and injecting air thru the other wells in the line so as to move a combustion front from well to well in the line, thereby establishing a combustion zone extending completely along the line of ignition wells. Injection of iron carbonyl with the injected air in this ignition step is practical and decreases the time required to establish the combustion zone across the line of wells. After this phase of the process has been completed, the production of the stratum each side of the line of wells is effected by injecting air containing iron carbonyl thru a line of injection wells on each side of the line of ignition wells and generally parallel thereto so that blocks of stratum on each side of the line of ignition wells are being produced simultaneously.

Other well patterns and modes of operation utilizing iron carbonyl in the inversely injected air are within the' scope of the invention.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A process for producing a permeable stratum containing hydrocarbons by in situ combustion comprising igniting a section of said stratum around an ignition well therein to establish a combustion zone; feeding a combustion-supporting gas to the ignited section thru said stratum from an injection area radially spaced from said well so as to burn a portion of the hydrocarbons and drive another portion therefrom; simultaneously feeding iron carbonyl dispersed in said gas into said section whereby said carbonyl decomposes to Fe and CO and said Fe catalyzes the combustion reaction; and recovering hydrocarbons produced by the combustion.

2. The process of claim 1 wherein air and iron carbonyl in vapor form are mixed and injected into said section as said combustion supporting gas.

3. The process of claim 2 wherein iron pentacarbonyl is incorporated in the injected gas.

4. A process for producing hydrocarbons from a permeable carbonaceous stratum which comprises igniting said stratum around at least one ignition well to form a combustion zone therein; injecting air admixed with iron carbonyl in vapor form into said stratum thru at least one otlset injection well so as to force same into said combustion zone whereby said iron carbonyl decomposes to Fe and CO and said Fe catalyzes the combustion reaction; and recovering hydrocarbons from said ignition borehole driven out of said stratum by the combustion.

5. The process of claim 4 wherein iron pentacarbonyl is incorporated in the injected gas.

6. The process of claim 4 wherein a plurality of said injection wells surround said ignition well in a ring pattern.

7. The process of claim 4 wherein said stratum is ignited around each of a line of ignition wells and said mixture of air and iron carbonyl is injected thru a line of injection wells offset from and generally parallel to said line of ignition wells.

References Qiterl in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR PRODUCING A PERMEABLE STRATUM CONTAINING HYDROCARBONS BY IN SITU COMBUSTION COMPRISING IGNITING A SECTION OF SAID STRATUM AROUND AN IGNITION WELL THEREIN TO ESTABLISH A COMBUSTION ZONE; FEEDING A COMBUSTION-SUPPORTING GAS TO THE IGNITED SECTION THRU SAID STRATUM FROM AN INJECTION AREA RADIALLY SPACED FROM SAID WELL SO AS TO BURN A PORTION OF THE HYDROCARBONS AND DRIVE ANOTHER PORTION THEREFROM; SIMULTANEOUSLY FEEDING IRON CARRBONYL DISPERSED IN SAID GAS INTO SAID SECTION WHEREBY SAID CARBONYL DECOMPOSES TO FE AND CO AND SAID FE CATALYZES THE COMBUSTION REACTION; AND RECOVERING HYDROCARBONS PRODUCED BY THE COMBUSTION. 